The present invention relates to the detection of defects in railway track rails.
Railway track rails can develop a number of different defects/flaws/faults during manufacturing and/or during the operational life time of the rails. There are a number of different types of defects, and the International Union of Railways (UIC) has defined a standard system for classifying broken, cracked and damaged rails.
UK patent application GB 2 383 413 describes a system for detecting rail defects using acoustic surface waves. This prior art system comprises an ultrasonic transmit transducer and a plurality of receive transducers positioned along the rail at different distances from the transducer. A degree of probability that there is a fault at a rail location is computed from measured changes in the spectral components of a surface wave.
It is a disadvantage of the above prior art technique that it requires contact of the transducers with the rail.
The article “Laser ultrasonic detection of rail defects” by Shi-Chang Wooh et al., in Review of Quantitative Nondestructive Evaluation, Vol. 21, ed. By D. O. Thompson et al., pp. 1819-1826, American Institute of Physics, 2002, discloses a method of characterising rail defects using a laser ultrasonic scanning technique and by analysing shadow patterns produced by shear waves. Even though this method provides a non-contact detection and characterisation of transverse defects in the rail head, this prior art method is limited to the detection of a certain defect type.